Lights are often used to display information, including information warning of a potentially dangerous condition. For example, brake lights on a motor vehicle are intended to alert those following that the vehicle in front is slowing or has stopped. Aircraft wing-tip strobe lights are intended to alert other pilots to the presence and direction of the aircraft. Lights are often used with machinery to provide warnings, for example, an automobile dashboard light that turns on to warn a motorist of low tire pressure, low brake pressure, and the like (so-called "telltale" lights). Lights are often used to warn of a stationary hazard, e.g., a flashing hazard light unit placed near an open hole in a roadway.
As used herein, the terms "light" or "light source" denote a source of luminous energy. Thus, "light" or "light source" can include, without limitation, incandescent bulbs, gas discharge tubes, fluorescent lamps, cathode ray tubes, liquid crystal displays, lasers, as well as solid state light-emitting-diodes ("LEDs").
When used as a warning device, a light should be perceived by an observer at the earliest possible moment. By "perceive", it is meant that an observer not only experiences a sensation due to the luminous energy from the light, but that the luminous energy immediately attracts the observer's attention. Thus, motor vehicle brake lights should, ideally, operate such that a motorist following perceives the luminous energy from the lights, recognizes that braking has occurred, and immediately begins evasive action, e.g., braking and/or steering. If the following vehicle is travelling at 55 mph, in one second 80' or 24 m will be covered. At that speed, if the vehicle in front suddenly brakes, or if a stationary hazard is suddenly encountered, a delay of perhaps only 50 ms in responding to the brake or warning light may determine whether a collision or a near miss results. In short, it is desired that an observer not merely "see" another vehicle's brake lights, or hazard warning lights, but that the observer perceive with minimal delay that the object ahead is looming ever closer.
Of course environmental degradation can interfere with the ability of observer to perceive warning or hazard lights. For example, it may be raining, the air may be foggy or dusty, there may be dust on the braking vehicle's brake lights or on the following vehicle's windshield. Further, the intensity of luminous energy from the brake lights might be diminished, perhaps from increased wiring resistance due to corrosion. All of these effects tend to veil the brake or warning light.
Dynamic looming visual information is also important in aviation. Federal law dictates that aircraft be provided with warning wing-tip lights that flash in unison, typically with a repetition rate of about one to two flashes per second. U.S. Pat. No. 3,903,501 to Greenlee et al. discloses the use of left wing and right pairs of for ward-facing wing tip lights that are used with left and right wing rearward-facing wing tip lights. On each wing, one of the pair of lights flashes synchronously with the corresponding rearward-facing light and approximately 175 ms later, the remaining light in each pair is flashed. The resultant double flashing pattern is stated to improve collision avoidance. It appears that Greenlee et al. would function equally well using a single for ward-facing light in each wing tip that flashes in synchronism with the rearward-facing light and flashes again 175 ms later. However, given the age of Greenlee et al., it is possible that gas discharge tube aircraft lights available at the time were not fast enough to double flash within 175 ms.
Even when looming type information is not critical, rapid recognition of luminous energy from a warning light can still be important. For example, if a dashboard mounted flashing LED that warns of low brake pressure or low tire pressure is not perceived in time by the motorist, damage to the motor vehicle can result. Similarly, lights may be used to demarcate highway lane edges. Future highways contemplated under the Intelligent Vehicle Highway System ("IVHS"), will have dramatically lessened lane widths. Thus, safe use of such future highways dictates that warnings of incursion by a vehicle upon the lane edge be heeded instantaneously.
Having described some general applications for warning lights, the physiology of visual detection will now be described briefly.
The sense of sight generally involves perception of form, color, size, movement and distance of objects. Stimuli in the form of visible luminous energy rays enter the eyes of an observer and form images on the retina. Cells in the retina absorb the luminous energy rays, are altered thereby, and generate electrical signals. Some of these signals are known to lead to nerve responses in subsequent neural ganglion cells. The axon portion of the ganglion cells carries information in the form of electrical impulses through optic nerve fibers to the lateral geniculate nucleus, and then to the visual cortex region of the brain. The visual cortex includes a projection region having a map-like correspondence to points on the retina, and thus to points in visual space.
Researchers generally classify the retinal ganglion cells as projecting to relatively large magnocellular cells ("M cells") or to smaller parvocelluar cells ("P cells") of the lateral geniculate. Especially relevant to the present invention, retinal M cells have a thicker axon than do P cells, which thickness permits neural impulses from M cells to travel more quickly to the brain than impulses from P cells. M cells also respond well to visual stimuli that are rapidly turned on and off, and to moving stimuli.
Thus, it is known in the relevant art that M cells have better function than P cells for recognizing transient visual stimuli, especially rapidly moving objects. It is also interesting to note that victims of certain ophthalmic disease, e.g., glaucoma, appear to initially suffer a degradation of M cell function. However, outside of the research laboratory, an effective procedure for testing for the onset of glaucoma by presenting a patient with stimuli intended to elicit M cell response is not yet in standard practice.
In summary, there is a need for a method and apparatus to enhance warning or hazard light visibility, to hasten viewer perception of such lights, and to improve salience. Because the human visual system appears to respond more rapidly to perceived object movement than to a stationary object, such method and apparatus preferably should stimulate and elicit such a response. In a dynamic warning application, preferably the light source should present a looming image that enhances and hastens the viewer's perception of approaching danger. Further, even in non-warning or hazard environments, there is a need for a visual display having an enhanced likelihood of capturing even a casual viewer's attention. Moreover, it is desirable to provide a warning signal whose visibility is resistant to the sensitivity-lowering effects of blur. Finally, there is a need for a method and apparatus to promote earlier detection of eye disease such as glaucoma that initially attacks a patient's M cells.
The present invention provides such methods and apparatuses.